Hinges are often used in industry to connect components movably to each other. The hinges are intended to allow movements and transfers of force in certain directions, but prevent them in other directions. An example of this is a solid body or flexure hinge. In this case two material segments that are connected to each other monolithically are provided with a material tapering (a so-called “thin spot”) in order to enable movements about a pivot axis formed by the thin spot. Pivoting movements about axes perpendicular thereto and translatory relative movements of the two material segments, however, are prevented.
Such flexure hinges are known in particular from modern weighing technology, which utilizes monolithic link arm mechanisms, so-called monoblocks. Through this, production costs are reduced and the precision, reproducibility, and long term stability are improved at the same time. In the case of the monoblocks for balances, thin spots are used, among other places, as hinges for parallelogram arms, for levers, and on coupling rods. In the case of balances that operate on the principle of electromagnetic force compensation, the deflections of the levers or parallel arms are as a rule very small, so that only small pivot angles arise at the hinges.
Processes known for production of thin spots on monoblocks include chip-cutting processes, but erosion (wire erosion) and laser beam machining are also known techniques.
A thin spot has the task of reliably transferring tensile and compressive forces in the form of normal stresses. On the other hand, the thin spot is intended to produce as low as possible a resistance to pivoting about its pivot axis and the bending stiffness about the pivot axis should therefore be as low as possible. This is why the desire is to remove as much material as possible in the region of the thin spot (reduction of the bending stiffness), while maintaining a minimum strength, in particular for normal stresses. To achieve this, the solutions known from the prior art either seek to reduce the cross section of the thin spot further, where the reduction is kept constant over the entire width of the block, or the width of the thin spot is reduced further by, for example, recesses disposed centrally on the pivot axis of the thin spot. Through-holes or drillings (as shown in JP2004340593 A1 and U.S. Pat. No. 7,307,226 B2) or troughs or depressions (as shown in DE 10 2013 108 097 B4 and DE 100 15 311 B4) are known. In any case, besides the desired reduction of the stiffness, the stability (load capacity, strength) is always undesirably reduced, even if it is represented as “acceptable” in the literature.
It is disadvantageous with these known solutions that with a decrease of the bending stiffness, the strength with respect to normal stresses becomes reduced, and vice versa. Moreover, due to material removal, in particular in the thin spot, regions with increased or decreased material stress (hot spots) always result.